A thorough understanding of the abilities of normal-hearing and hearing- impaired individuals to perceive spectral-temporal properties of speech is lacking. In particular, the relation between the basic capabilities of the auditory system to process speech and the perception of speech in normal discourse is poorly understood. Proposed extensions of our previous research should help remedy this need. The first line of research uses psychophysical techniques to determine listener abilities to detect, discriminate, and identify vowels, including modeling of the peripheral auditory processing of these complex sounds. The outcome of these experiments will provide detailed knowledge of the peripheral processing of vowels, as well as the influence of more centrally located processes (e.g. memory). Additional discrimination studies ill examine: (1) the influence of gender-related properties of the glottal source on vowel formants; and (2) the effects of the dynamic variation of formants observed in normal English vowels. Models of auditory processing that provide a detailed description of the psychophysical properties of vowels will be developed. The focus of the project is to gain detailed knowledge of one of the most salient properties of speech, vowels, in normal-hearing persons. Selected studies will be extended to include hearing-impaired persons to examine the negative effects of hearing loss on speech reception and their possible remediation through amplification.